We have measured the partial width and forward-backward charge asymmetry for the reaction e + e - →Z 0 →μ + μ - (γ). We obtain a partial width Γ μμ of 83.3±1.3(stat)±0.9(sys) MeV and the following values for the vector and axial vector couplings: g v =−0.062 −0.015 +0.020 and g A =−0.497 −0.005 +0.005 . From our measurement of the partial width and the mass of the Z 0 boson we determine the effective electroweak mixing angle, sin 2 θ w =0.232±0.005, and the neutral current coupling strength parameter, ϱ =0.998±0.016.
Forward backward charge asymmetry.
None
No description provided.
We report on total cross section and forward backward charge asymmetry measurements of the reactione+e− → τ+τ− at centre of mass energies of 35.0 GeV and 42.4 GeV using the TASSO detector. Including previous data an analysis in terms of electroweak parameters of the standard model is presented, and lower limits on mass scale parameters of residual contact interactions are given. A combined analysis of electroweak couplings using all our results on leptonic reactionse+e−→l+l− has been performed.
No description provided.
The reactione+e−→µ+µ− has been studied at centre of mass energies between 35.0 and 46.8 GeV using the TASSO detector at PETRA. We present measurements of the forward-backward charge asymmetry (Aμμ) and cross section σμμ for this reaction at three energies. At 35.0 GeV we obtain a cross section relative to the QED prediction ofRμμ=σμμ/σo=0.932±0.018±0.044 andAμμ=(−10.6−2.3+2.2±0.5)%. At 38.3 GeV we findRμμ=0.951±0.072−0.057+0.063 andAμμ=(+1.7−8.6+8.5±0.5)%. At 43.6 GeV we measureRμμ=0.921±0.037±0.055 andAμμ=(−17.6−4.3+4.4±0.5)%. Our results are in good agreement with the predictions of the standard model. Including previous TASSO data we present improved determinations of muonic electroweak parameters. We also report on lower limits of possible contributions from contact interactions.
No description provided.
High p ⊥ inclusive muon events produced in e + e − annihilations at √ s =29 GeV have been analyzed to obtain a measurement of the b b forward-backward charge asymmetry. The result A b =0.034±0.070±0.035 differs from the theoretical expectation (−0.16) unless substantial B 0 B 0 mixing is assumed.
No description provided.
We have measured the forward-backward asymmetry in Z 0 → b b decays using hadronic events containing muons and electrons. The data sample corresponds to 118 200 hadronic events at √ s ≈ M z . From a fit to the single and dilepton p and P ⊥ spectra, we determine A b b =0.130 −0.042 +0.044 including the correction for B 0 − B 0 mixing.
Observed asymmetry from fit to single and dilepton P and PT spectra assuming no mixing.
Asymmetry corrected for the effects of mixing using the L3 observed mixing parameter chi(B) = 0.178 +0.049,-0.040.
We present a measurement of the forward-backward charge asymmetry in hadronic decays of the Z 0 using data collected with the OPAL detector at LEP. The forward-backward charge asymmetry was measured using a weight function method which gave the number of forward events on a statistical basis. In a data sample of 448 942 hadronic Z 0 decays, we have observed a charge asymmetry of A h = 0.040±0.004 (stat.)±0.006 (syst.)±0.002 (B 0 B 0 mix.), taking into account the effect of B 0 B 0 mixing. In the framework of the standard model, this asymmetry corresponds to an effective weak mixing angle averaged over five quark flavours of sin 2 θ W = 0.2321 ± 0.0017 ( stat. ) ± 0.0027 ( syst. ) ± 0.0009 (B 0 B 0 mix.). The result agrees with the value obtained from the Z 0 line shape and lepton pair forward-backward asymmetry.
No description provided.
The second systematic error is due to the uncertainty in the correction for B.BBAR mixing which had been applied to the data.
A measurement of the charm and bottom forward-backward asymmetry in e+e− annihilations is presented at energies on and around the peak of the Z0 resonance. Decays of the Z0 into charm and bottom quarks are tagged using D mesons identified in about 4 million hadronic decays of the Z0 boson recorded with the OPAL detector at LEP between 1990 and 1995. Approximately 33000 D mesons are tagged in seven different decay modes. From these the charm and bottom asymmetries are measured in three energy ranges around the Z0 peak: \(\matrix {A_{\rm FB}^{\rm c}=0.039\pm 0.051\pm 0.009\cr A_{\rm FB}^{\rm c}=0.063\pm 0.012\pm 0.006\cr A_{\rm FB}^{\rm c}=0.158\pm 0.041\pm 0.011}\)\(\matrix {A_{\rm FB}^{\rm b}=0.086\pm 0.108\pm 0.029\cr A_{\rm FB}^{\rm b}=0.094\pm 0.027\pm 0.022\cr A_{\rm FB}^{\rm b}=0.021\pm 0.090\pm 0.026}\)\(\matrix{\langle E_{cm}\rangle =89.45\ {\rm GeV}\cr \langle E_{cm}\rangle =91.22\ {\rm GeV}\cr \langle E_{cm}\rangle =93.00\ {\rm GeV}}\) The results are in agreement with the predictions of the standard model and other measurements at LEP.
Forward-backward asymmetry.
The$\tau$polarisation has been studied with the${\rm e^+e^-}\to \tau^+\tau^-$data collected by the DELPHI detector at LEP in
No description provided.
A measurement of theτ lepton polarization and its forward-backward asymmetry at the Z0 resonance using the OPAL detector is described. The measurement is based on analyses of τ→ρντ, ττπ(K)ντ,\(\tau\to e\bar \nu _e \nu _\tau\),\(\tau\to \mu \bar \nu _\mu\nu _\tau\) andτ→a1ντ decays from a sample of 89075 e+e−→τ+τ− candidates corresponding to an integrated luminosity of 117 pb−1. Assuming that theτ lepton decays according to V-A theory, we measure the averageτ polarization at √s=MZ to be 〈P〉=(−13.0±0.9±0.9)% and theτ polarization forward-backward asymmetry to be ApolFB=(−9.4±1.0±0.4)%, where the first error is statistical and the second systematic. These results are consistent with the hypothesis of lepton universality and, when combined, can be expressed as a measurement of sin2θefflept=0.2334±0.0012 within the context of the Standard Model.
No description provided.
Forum